1. Field of the Invention
The present invention relates generally to semiconductor fabrication methods and, more particularly, to providing a self-aligned contact between two MOS transistors.
2. Description of Related Art
Fabrication of memory arrays conventionally employs the use of self-aligned contacts when high density is desired. One type of self-aligned contact takes the form of a salicide layer formed on a polysilicon gate of a MOS transistor. Another type of self-aligned contact takes the form of conducting material that connects a substrate to a metal layer disposed above a MOS transistor in an integrated circuit. A polycide has been used to form a self-aligned contact in these situations.
One commonly used polycide is tungsten silicide. Tungsten silicide may perform adequately in applications with larger geometries. However, as the density of memory arrays increases, the relatively high resistivity of tungsten silicide may preclude its use in nanometer process technologies.
Silicides with lower resistivity such as titanium silicide, cobalt silicide, and nickel silicide are available. These lower resistivity silicides could be candidates for replacing tungsten silicide in nanometer applications. Unfortunately, however, these lower resistivity silicides may not be suitable for use in many prior art applications, such as polycide techniques, because of their lack of high temperature stability.
A need thus exists in the prior art for an improved method of forming a self-aligned contact in high-density memory arrays. A further need exists for forming a self-aligned contact from materials lacking in high temperature stability.